1. Field of the Invention
The present invention relates to the stabilization of an enzyme-labeled anti-human interferon-.beta. antibody which may be used for an immunological microassay of human interferon-.beta., and more particularly to a freeze-dried composition which is capable of stabilizing an enzyme-labeled anti-human interferon-.beta. antibody over a long period of time. The present invention further relates to an enzyme immunoassay kit comprising such a freeze-dried composition.
2. Prior Art
When a trace amount of substance such as a protein, a peptide hormone etc. contained in a biological material such as serum, urine or the like will be measured, the method for measuring it requires a high sensitivity and high specificity. As a method for measuring used for this purpose, an immunoassay which utilizes an antigen-antibody reaction is well known.
The immunoassay may be classified into a competitive method and a non-competitive method. In the former, a sample liquid to be measured containing the antigen or antibody, which is a substance to be measured, is mixed with a substance to be measured which was pre-labeled and had a known concentration, and then the antibody or antigen is added to the mixture to form an antigen-antibody complex. By measuring a ratio of the labeled substance to be measured and the substance to be measured, each of which was involved in the complex formation, a content of the substance to be measured can be calculated. In the latter method known as a sandwich method, on the other hand, a first antibody is first bound to a solid phase, and then a sample liquid to be measured containing an antigen, which is a substance to be measured, is brought into contact therewith to bind the antigen to the first antibody on the solid phase, the solid phase being thereafter separated from the liquid phase. By the antigen-antibody reaction, a labeled second antibody is then bound to the antigen which is a substance to be measured and has been bound to the first antibody on the solid phase, and thereby an amount of the antigen to be measured can be determined after measuring an amount of the bound labeled antibody.
In accordance with the labeled substance used, the immunoassay may be divided into, for example, radio immunoassay utilizing a labeling agent of radioactive substance and enzyme immunoassay utilizing a labeling agent of enzyme. The enzyme immunoassay has recently come into wide use for such as ordinary clinical examinations because the assay has a sufficiently measurable sensitivity and a simple operability and is exempt from troublesome disposal after use.
However, an enzyme-labeled antibody or antigen has a problem of the long-term stability in a freeze-dried state for practical use. Therefore, the development of an enzyme-labeled antibody or enzyme-labeled antigen in which the enzyme activity is not lowered during the long storage has been demanded. Generally, an activity which is determined immediately after the preparation of the enzyme-labeled anti-human interferon-.beta. antibody as the enzyme-labeled antibody is lost by 50% at room temperature about 2 days after the preparation thereof, and substantially all the activity is lost 7 days thereafter.